<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        class Father {
            constructor(x, y) {
                this.x = x
                this.y = y
            }
            sum() {
                console.log(this.x + this.y);
            }
        }
        class Son extends Father {
            constructor(x, y) {
                super(x, y)
                this.x = x
                this.y = y

            }
            cun() {
                console.log(this.x - this.y);
            }
        }
        var son = new Son(5, 3)
        son.cun()
        son.sum()
    </script>
</body>

</html>